The present invention relates to a miniature radio receiver and, more particularly, to a miniature radio receiver having an antenna which is integrated with the housing thereof.
An antenna of the type constituting a part of the housing of a radio receiver is disclosed in, for example, U.S. Pat. No. 3,736,591 to Rennels et al, issued May 29, 1973. The antenna disclosed in this patent is constructed to serve as a loop antenna. The radiation principle of a loop antenna is as follows (the radiation principle is reversible for reception).
The electric field extending from a loop antenna to a location which is remote from the antenna by a given distance is defined by the combination of two different electric fields. One field is derived from a difference in phase between radiation currents flowing through two conductive arms of a U-shaped member. The other field is derived from a radiation current flowing through a conductive connecting portion of the U-shaped member. Hence, as the length of the connecting portion is reduced, i.e., as the thickness of the housing is reduced, the radiation currents through the two arms approach opposite phases with respect to each other. At the same time, the radiation current through the connecting portion is reduced, thus preventing a desired antenna gain from being attained. For this reason, the receiver structure shown and described in the above patent is not applicable to a receiver having a thickness which is less than 5 millimeters, i.e. a so-called card-type of receiver.
Japanese Laid-Open Patent Publication (Kokai) No. 57-103406/1982 (published June 28, 1982) teaches a portable radio apparatus in which a conductive plate is provided on the outer periphery of the housing to serve as a slit or slot antenna. A problem with this kind of radio apparatus is that the slot antenna mounted on the other periphery of the apparatus prevents the apparatus from being reduced in thickness.